1. Field of the Invention
This invention relates to the casting of metals, especially metal alloys with low melting points. More particularly, the present invention is directed to apparatus for use in casting metals and especially apparatus having a melt container connected to a casting mold by a casting line. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
Casting methods and apparatus, wherein molten metal is conveyed from a furnace or melt container to a mold(s) via casting line(s), are known in the art and, for example, are used in the production of dead cores for plastic injection-molded parts, like those used in the automobile industry. Safety considerations dictate that molten metal not be allowed to free fall into an open mold. Accordingly, casting molds are usually filled from below through a pressurized casting line. The pressure in the line is maintained until the metal has completely hardened in the casting mold. In order to enable removal of the hardened part from the mold, or to change the tool, the connection between the casting line and the casting mold must be broken in a manner that prevents spillage of liquid metal in the line. At the same time, however, to save time for the next casting process and to avoid deposits on the walls of the casting line, the casting line should not be completely emptied. Accordingly, the vertical level of the molten metal in the casting line is adjusted so that it is stabilized at a height which is slightly below the dividing line between the casting mold and the casting line.
In the prior art, it is common practice for the metal level in the system to be established by means of a standpipe. An overflow hole, which can be opened by an overflow valve, is provided in the standpipe at a height corresponding to the desired level of the molten metal. After the end of the casting process, the overflow valve is opened to permit excess metal to flow off. The casting line and the standpipe are in fluid communication so that the level of metal in the casting line cannot fall below the level defined by the overflow hole in the standpipe. The melt is kept from flowing from the casting line back to its source, i.e., into the melt container, by a check valve.
The standpipe of the above-described prior art system is arranged outside the melt container. The standpipe must, accordingly, be heated to prevent the melt from hardening in the standpipe. Economics dictate that the melt flowing off through the overflow hole be fed back into the melt container. During the flow back to the melt container, the liquid metal comes into contact with air and may oxidize. Oxides delivered into the melt may have an adverse influence on the quality of the melt.